"Either you are suggesting the a/c was descending at 'way outside' 20 000 fpm, or you don't understand the notion of radalt 'tracking capability'. I assume the latter."

If you are claiming the tracking capability is based on terrain closure, ie, in the vertical, when flying at 330 fps and level, anything with a rise in terrain of 45 deg slope will out run the tracking capability. This includes buldings which have 90 degree "slopes".

The faster you go, the less slope in terrain that will be required to outrun the tracking capability.

You don't have to be descending for terrain to rise to you. The speed at which terrain rises to your altitude is a function of your forward speed.

The tracking capability is based on forward motion of the aircraft. These radalt's are used for low and slow approaches. They are not TFR radalts as used by Fighter and Attack aircraft following terrain.

As for pressure altimeters, which comment in particular are you referring to? That they are required for IFR flight and a radlat is not? Do you feel the static system in a standard 757 is not calibrated to .86 mach?

A320,
"It depends on what you are measuring as to which instrument to use. The Radalt isn't even required for IFR flight but a pressure altimeter is. Why does the FAA require the use of a Sensitive Pressure Altimeter over a Radalt for IFR flight? When you understand this question, you will understand the answers you have been given here from pilots."

Well it is obvious - if you only have one instrument it has to be the altimeter as radalt does not work above 2500 feet above ground level.

"Why do you prefer radalt over pressure altitude when the NTSB lists radalt as ":not working or unconfirmed","

The radalt appears to be working as ground proximity warning was working. Only radalt provides that.

"the radalt is traveling way outside it's tracking capability of 330 fps,"

The vertical speed was much less than 330 fps.

" and the objects it is measuring from is unknown?"

You can see what is was measuring from by counting back from the impact point where the longitudinal acceleration went strongly negative. There are no buildings there to confuse it. I think you are confused. How do you account for the strong longitudinal acceleration if the plane did not hit?

"Furthermore, the NTSB lists Pressure Altitude as "working and confirmed" and is operating well within it's calibration rated to M0.86."

We have covered this. At high altitude the pressure altimeter would no doubt be calibrated to M 0.86 but at low altitude the plane is not allowed to fly that fast so why would it be calibrated to M 0.86? In fact, how could they do the low altitude tests to determine the calibration errors at speeds beyond which the plane is permitted to fly?

I notice that you are very adept at finding statements on the Pilots for 9/11 Truth website. I suspect you are a member. I suspect you personally think the plane flew over the Pentagon. Do you think the last radalt recording was from the roof of the Pentagon?

"the radalt is traveling way outside it's tracking capability of 330 fps,"

The vertical speed was much less than 330 fps.

Radalt tracking capability is not based on the vertical closure rate with terrain. It is based on the forward motion of the aircraft. Forward motion of the aircraft, combined with slope of terrain, determines aircraft closure rate with the ground. If your theory were correct, you would not get a GPWS on terrain sloping up to you which has a more than a 45 degree slope if you were flying level at 330 fps (roughly 195 knots).

If you were flying level at 400 knots, the terrain will outrun the radalt tracking capability on a mere 27 degree slope, if your theory were correct. It's not.

Furthermore, the usual angular limits (not tracking capability) of a radalt are 30 deg bank and 15 deg pitch. In other words, you will not get a Radlt reading if you are descending over 15 degree pitch or rolling into more than a 30 deg bank.

At 330 fps forward speed (~ 195 knots) and more than 5,200 fpm (roughly 85 fps descent rate) you will not get a radalt reading as this is more than a 15 degree angle and the radalt is no longer "painting" the ground, it is shooting off to the horizon due to descent angle.. Someone mentioned these limits earlier in this thread.

Gravity - I wouldn't bother with your mission. Because when dealing with conspiracy prats, they'll tell you that the data has been 'got at' or that someone else has snuck into Boeing and changed the calibration specs. Remember, when you start arguing with idiots, they'll drag you down to their level and beat you with experience. Instead, I'd set them off looking for the 'Extra-Terrestrials' who were really flying the plane or along the line that the whole thing was organised by those who had the most to gain - the security industry.

I have been aware of the paper by Legge and Stutt for some time. I found the paper to be logical. I saw that the discrepancy between the radalt and the pressure data was so large that even if they had made some error in calculation, there was no way the two readings could be in agreement. So it boils down to which is the more reliable.

Everyone on this thread confirms that the radalt will be accurate in this case because the plane is not tilted, is not closing too rapidly with the terrain and, close to impact, is not passing over significant buildings or steeply sloping ground.

Everyone on this thread assures me that there are numerous reasons why the pressure data could be corrupted. The plane is certainly flying faster that its permitted speed, and that is a likely cause of error.

So it seems rather odd that you favour the pressure altitude over radalt.

I remind you that the people on this thread are mostly experienced pilots. I suggest you reconsider the evidence, consult with pilots and mathematicians who are not members of Pilots for 9/11 Truth, and see what you can come up with if you start afresh.

I think you misunderstood the posts made on this thread with respect to radalt being more "accurate" than Pressure altitude.. Here they are again -

skwinty - post 4 -

Quote:

The cause is that they are two different types of instruments that operate on totally different principles and measure two distinctly different parameters

MadFLT - post 14 -

Quote:

Radalt measures distance to an object giving a radar return.

Altimeter uses pressure data to infer height above a reference datum.

You really can't compare the two. they aren't even really measuring the same thing. Depending on what you actually want to know, either may be better/"more accurate".

When you offered the speed on page 4 -

skwinty - post 63 -

Quote:

If the computer performs the calibration in flight, then the speed envelope should cover at least Mach .8 so the graph would show that as the upper velocity range.

ChristiannJ aka CJ - post 65 -

Quote:

But one well-known phenomenon on Concorde occurs when 'breaking the sound barrier', or better expressed, when accelerating past Mach 1. A shock wave then moves from the nose along the fuselage past the static ports. It's barely visible on the altimeter, but there is a very noticeable 'twitch' on the VSI (there are videos of that, and we've even managed to simulate it on the Brooklands Concorde simulator).

(added bold above)

Me - post 66 -

Quote:

the static systems on large transport aircraft are rated to the Mmo of that aircraft and corrected by the air data computer. This is why you will read a calibrated airspeed on most large transports and not an Indicated Airspeed. So the staitic system would be rated to .86 mach. To understand the reasons for Vmo/Mmo click here...

But the aircraft was well within the Pitot-Static calibration parameters rated to .86 Mach.

(added bold above)

CJ - post 69 -

Quote:

My back-of-the-envelope says M=0.74, assuming ISA.

Seems to be too far below M=0.86 to really matter

(added bold)

skwinty - post 73 -

Quote:

488 knots at 500 ft is completely outside of the normal flight envelope.

This, as confirmed by A320slave, does not imply that the pitot static was out of its calibration envelope.

(added bold)

Gravity32, if you feel the static system was experiencing error at M0.74, why wasn't the airspeed experiencing some type of error when Ram air is used to measure against static pressure for an airspeed indicator? According to you, the airspeed indicator should have disintegrated (or perhaps shown some type of error) at such high dynamic pressure. Unlike the Altimeter and VSI, the airspeed indicator has RAM AIR pushing directly into the system. But yet, it is working fine and correlates with groundspeed. It is working fine because the Pitot-static system is rated to M0.86.

Finally, you failed to answer my questions gravity32.

Please respond to these questions.

Do you agree with Frank Legge that the WTC was destroyed by controlled demolition? Specifically thermite? Yes or no.

Everyone but you on this thread confirms that the radalt will be accurate in this case because the plane is not tilted, is not closing too rapidly with the terrain and, close to impact, is not passing over significant buildings or steeply sloping ground. It was also proved reliable by checking every landing on the FDR file, and found to give -6 feet in every case while taxiing.

When you deal effectively with this, that the radalt is reliable, it will be time to discuss other matters.

Everyone but you on this thread confirms that the radalt will be accurate in this case because the plane is not tilted, is not closing too rapidly with the terrain and, close to impact, is not passing over significant buildings or steeply sloping ground. It was also proved reliable by checking every landing on the FDR file, and found to give -6 feet in every case while taxiing.

You started this thread claiming that the Pressure altimeter would not be accurate operating "outside of it's envelope".

Many agreed. I would agree too.

Then you posted the actual speed on page 4. See the above quotes. The Pitot-Static system was operating well within it's capability without error and is confirmed with airspeed v. groundspeed analysis as pointed out in this thread.

Do you think that Radalt only measures from the ground? What happens if a building is on the ground? Does the Radalt measure through that building to the ground?

If you feel Radalt tracking capability is based on vertical speed, how does that apply when crossing over multiple obstacles with a 90 degree side? Do you know basic trigonometry?

Do you think that Radalt only measures from the ground? What happens if a building is on the ground? Does the Radalt measure through that building to the ground?

A320, You clearly know enough about this crash to know that there were no buildings other than the Citgo service station in the vicinity. How high is that? It provides little more than a roof over the heads of customers. Your response is clearly an attempt to sidestep the reality. The reality is that the radalt can be trusted in this case.

Quote:

If you feel Radalt tracking capability is based on vertical speed, how does that apply when crossing over multiple obstacles with a 90 degree side? Do you know basic trigonometry?

You know enough about radalt to know that a plane passing over a city with many buildings with vertical sides has no problem providing correct guidance to pilots when they arrive at the airport. Again your response is just a sidestep.

Quote:

if you want to talk amongst real pilots, try not to use the word "tilted".... rather bank, roll, pitch, yaw, crab... etc.... these are the terms real pilots use.)

You don't have to be a pilot to know that "tilted" in one word covers all these angles. Again your response is a sidestep.

What we see is you making strenous efforts to sidestep the issue, that radalt can be trusted in this situation. It reminds me of the language I see at Pilots for 9/11 Truth. You should be careful who you copy.

For anyone who clicks my links combined with reading your posts here, they will understand you opened this thread to gain support of pressure altimeter error operating "outside pressure altimeter calibration".

After you disclosed the speed on page 4, every single pilot on this thread concluded that the pressure altimeter was not operating outside of it's calibrated envelope.

So let us put this into perspective..

The Radalt was operating more than 2x outside of it's tracking capability according to the data.

You seem to think that the tracking capability is based on vertical closure rate with terrain and/or any obstacles on the terrain. You are wrong. Trigonometry proves you wrong.

Here is another lesson in aviation terminology. When one talks of "tracking" or "track", it is the track of the aircraft over the ground. Not the vertical speed of the aircraft..

For example, according to your claim that radalt tracking capability is based on vertical speed, if the aircraft were traveling at 250 knots (422 fps forward speed) with a descent rate of 320 fps (19,200 fpm), you are implying that the radalt could track this measurement because the vertical descent rate is less than 330 fps tracking capability..

Pilots here will understand how absurd this notion is as the angle of descent is almost 50 degrees.

Given the links I have provided above, and the replies given by the pilots here, I guarantee you will not find one pilot to sign their name to your next paper, just like you have not been able to find one to sign their name to your last 3 papers over the past 3 years, including your papers prior which claim the WTC was demolished by the use of themate.

You will not gain "influence" among the circles you are attempting to influence. You lose credibility each time you attempt to discredit real and verified pilots. Keep up the good work!

For anyone who clicks my links combined with reading your posts here, they will understand you opened this thread to gain support of pressure altimeter error operating "outside pressure altimeter calibration".

True, but I soon learned here that most of these experienced pilots agreed that there was no reason to suspect the radalt would be wrong, and therefore it must have been the pressure altitude that was wrong.

Quote:

After you disclosed the speed on page 4, every single pilot on this thread concluded that the pressure altimeter was not operating outside of it's calibrated envelope.

False. Obviously it would be calibrated at the observed speed, 488 knots, at high altitude, but at 50 feet above sea level the plane couldn't be legally flown, so couldn't be test flown, so one would think it couldn't be calibrated. Can you explain how it could be calibrated at a speed far above its legal maximum speed? What grounds are there for claiming that a calibration in thin high altitude air can be applied in dense sea level air?

Quote:

So let us put this into perspective.. The Radalt was operating more than 2x outside of it's tracking capability according to the data.

You have not provided any source for your claim that the manufacturer's limitation is for horizontal velocity. The plane only moves a tiny fraction of a millimeter in the time it takes for the signal to reach the ground and be reflected back. How can there be any limit to horizontal capability? One concludes this is a false claim.

Quote:

For example, according to your claim that radalt tracking capability is based on vertical speed, if the aircraft were traveling at 250 knots (422 fps forward speed) with a descent rate of 320 fps (19,200 fpm), you are implying that the radalt could track this measurement because the vertical descent rate is less than 330 fps tracking capability..Pilots here will understand how absurd this notion is as the angle of descent is almost 50 degrees.

The plane was only descending at about 50 feet per second, 3000 feet per minute. I think pilots here will agree that they can safely depend on the radalt at that rate of descent and will find your discussion of an "almost 50 degree" angle irrelevant.

By the way, are you the same A320Slave who came to this site in 2008 to try to get people to agree that AA77 would not have been able to get its position reports correct if it started its flight without entering its exact position prior to moving? Did you not believe John Farmer when he provided on overlay of the radar track and the FDR track, which showed the two tracks converging after the plane had been in the air for a few minutes, and presumably in reach of DME and VOR signals?

Now that I have learned who "gravity32" actually is, It is pointless to continue this discussion beyond this reply.

Gravity32 -

You make the statement -

"You have not provided any source for your claim that the manufacturer's limitation is for horizontal velocity."

Gravity32, you have made the claim that 330 fps tracking capability is based on vertical speed and have not provided any source for your claim. 330 fps is roughly 20,000 fpm.

Please let us know when you find one real and verified pilot who will agree with you that a 757 radalt can accurately measure True Altitude, absolute altitude, any altitude... at anything below 20,000 fpm (330 fps) descent rate.

To keep this even more simple, please let us know when you find one pilot who will endorse your claims that a radalt can measure precisely at a descent rate of perhaps 10,000 fpm. Less than half the radalt tracking capability according to your vertical speed theory..

I believe someone above mentioned, "Never wrestle with a pig, they'll only drag you down to their level".

I agree wholeheartedly.

Gravity32, anytime you wish to answer my questions and/or get a real and verified pilot to support your absurd claims with respect to aviation, including your WTC claims of controlled demolition based on thermate, let us know. Until then, this argument is like (to a layman) a 45 year old arguing with a 12 yr old on how to drive a car.

Please let us know when you find one real and verified pilot who will agree with you that a 757 radalt can accurately measure True Altitude, absolute altitude, any altitude... at anything below 20,000 fpm (330 fps) descent rate.

There is a great deal I don't know about aviation and I get some things wrong. I am happy to ask for advice. That is why I am here. But I do not take advice from just anyone.

For instance I would be reluctant to take advice from someone who thought that AA77 would experience an unsurvivable wing load of 10.14g as it pulled out of its dive on approach to the Pentagon. That is what the experts at Pilots for 9/11 Truth are telling the public. Several other people have calculated a wing load of less than 2g. That is very different. I have checked the calculation myself and have found it could be as low as 1.7g depending on the actual course taken. I have informed Rob Balsamo of the error in his calculation but he makes no change to the site and makes no apology to the public for missleading them. That is why I seek advice elsewhere.

Please let me know when you find one real and verified pilot who thinks radalt will not be accurate for a plane at a descent speed of 50 ft per second and levelling to almost level at the last radalt reading, not flying over buildings, not at a steep bank, pitch, or yaw, when only a few feet above the ground.